<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      div {
        border: 1px solid;
      }
    </style>
  </head>
  <body>
    <div id="box" hidden>hello <u>div</u></div>
    <script>
      const divEl = document.getElementById("box");
      console.log(divEl.hidden); //true
      setTimeout(() => {
        divEl.hidden = false;
      }, 3000);
    </script>
  </body>
</html>
